line dump

[Razzamattaz 0]

Hi, I was just wondering what the risk is on a line dump. I just saw a video of a tandem's main lines dumping on deployment. But the main still came out fine.

[billvon 2,998]

>Hi, I was just wondering what the risk is on a line dump.

When most people refer to line dump, they are actually referring to line dump/bag strip which is indeed a problem. If you pull on the canopy so hard and so suddenly that none of the lines can "keep up" they can pull out of the stows. If they pull out of the locking stows as well, the bag can be 'stripped' off the still-packed main before it's even to the end of the lines.

That's very bad, because the canopy is going to start to open amidst that nasty tangle of lines, and is going to be partially inflated before it even reaches the end of the lines. That can lead to incredibly hard openings; hard enough to destroy the canopy and/or harness.

A line dump that causes one or two line groups to fall off is not generally a problem in and of itself. Since the bag has to be accelerated very hard for this to happen, though, it's generally a symptom of another problem. That problem might be a PC that's too large or a too-high deployment speed. Those things may also lead to hard openings - but the line dump itself doesn't _cause_ the hard opening.

[Razzamattaz 0]

Cool, thanks 4 the reply.

[riggerrob 643]

I have suffered line dump several times with tandems. I have broken a few lines, torn a few canopies and suffered more tension knots than I care to remember. Several colleagues were forced to retire because of chronic shoulder, spine and hip injuries caused by hard openings on first generation (F-111) tandems.

All of the different tandem manufacturers have added extra stows to reduce the incidence of line dump.
Strong Enterprises adds three bungees to its Anti-Line-Slump flap. One problem is that packers tend to whine about stock bungees being so tight their fingers hurt, so they lengthen them so much that they become useless.

Relative Workshop uses double-wide rubber bands on civilian tandems and even stronger rubber bands on their (500 to 1,000 pound) military tandems, so strong that they caution civilians not to use military rubber bands for fear that they will cause bag lock.

Eclipse use a third row of rubber bands - on the center-line of the d-bag.

Jump Shack uses Speed Bags which effectively have a dozen locking stows, and the stows on Speed Bags are only half the width of the d-bag. This sort of "balanced line stow" is less likely to dump because the weight of the line stows is equal on both sides of the rubber bands.

[indradhanush 0]

being a tandem instructor i can tell you that often line dump causes becuse of not using good rubber bands/stow bands. as it said by Bill Morissy pack the line. if you keep a good stowing line dump should not be aproblem. if it is small canopy line dump definetely require a cut away....
Learn from the mistakes of others .....

life is a daring adventure or nothing at all

[billvon 2,998]

>This sort of "balanced line stow" is less likely to dump because the
>weight of the line stows is equal on both sides of the rubber bands.

And because each stow weighs half as much; the rubber band only has to hold half the weight.

[billbooth 10]

You will notice that from day one, Vector/Sigma tandem bags have four locking stows. The center two are very close together, yielding a "balanced" force on each side of the stow band. This has kept the canopy in the bag until line stretch pretty effectively for the past 23 years.

[riggerrob 643]

If the slider remains at the top of the lines, no big deal.

However, if the slider slumps/dumps at the same time as the lines, you will be in a world of hurt.
Discovering that your canopy is partially inflated when you reach line stretch will cause you a whole world of pain! ... broken lines! ... torn fabric! ... etc.

Trivia: there is a Russian-designed Rogallo reserve - called PZ-81 - that has no d-bag or diaper. However, its slider is tied to the pilot chute by a long bridle. The pilot chute "lifts" the canopy via the slider, so there can never be any slack - between the canopy and the slider - until after line stretch/late in the deployment process.

Historical note: there were several American-designed military freefall canopies that used similar pilot chute controlled sliders to soften openings at the heavy weights, high altitudes and high airspeeds of HALO/HAHO jumps.
A few civilian accuracy competitors also used pilot chute controlled cliders to soften openings on accuracy (precision landing) competition canopies.

[pilatus_p 0]

I recently had a hard opening, believed to be caused by line dump.

I sustained two broken ribs and two fractured vertebrae at t6 and 7.

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